The overall objective is to investigate and clarify pharmacological and physiological interrelationships between calcium and secretion and effects of calcemic hormones and gastrointestinal (GI) hormones. The goal is to relate the findings to calcium homeostasis and GI function in health and disease and to provide new knowledge to improve measures for the prevention, diagnosis, and treatment of calcium-and GI related disease. Emphasis will be placed on the secretion and actions of calcitonin (CT), parathyroid hormone (PTH), and gastrin, but the studies also will involve vitamin D metabolites and numerous GI hormonal peptides (e.g., CCK, secretin, somatostatin (SRIF), boebesin, GIP, substance P). Problems to be investigated: 1) In vivo in pigs: a) Effects of GI hormgnes on secretion of CT and PTH- temporal relationships and physiological significance; b) Effects of prostaglandins and catecholamines on CT, and gastrin secretion; c) Production of SRIF by the thyroid gland and gastric antrum. Physiological significance of inhibitory effect of SRIF on CT secretion; d) Interactions and physiological significance of PTH, CT, Ca, SRIF, and bombesin effects on gastrin secretion. 2) In vivo in the rat: a) Potential detrimental skeletal consequences of CT removal in early life; b) Application of RIA for rat PTH together with that for CT to compare hormonal changes throughout life, esp. during lactation and suckling; c) To extract and characterize the non-gastrin GI peptide which is a postprandial CT secretagogue in the rat. 3) In vitro studies of secretion of CT and PTH from rat thyroparathyroids to examine substances which affect their release and their mechanisms. 4) Development of RIAs for secretin and CCK to study these hormones and their interactions with calcemic hormones. 5) Studies of rat pituitaries to localize, and explore actions of the CT-like immunoreactive material there and compare it to CT. Related studies will compare actions of this material to those of authentic CT. 6) To explore actions of CT and PTH on bone cells and to compare activities of pituitary CT material to authentic CT.